The continuous casting of steel is a well-known process. It consists in pouring a liquid metal from a ladle into a tundish intended to regulate the flow and then, after this tundish, in pouring the metal into the upper part of a water-cooled bottomless copper mould undergoing a vertical reciprocating movement. The solidified semi finished product is extracted from the lower part of the mould by rollers. The liquid steel is introduced into the mould by means of a tubular duct called a nozzle placed between the tundish and the mould.
Document EP 0 269 180 B1 describes a specific continuous casting equipment called “Hollow Jet Nozzle” (see reference FIG. 1) in which the liquid metal is poured onto the top of a dome 2 made of a refractory material. The shape of this dome 2 causes the metal to flow towards its periphery, the flow being deflected towards the internal wall of the nozzle or of an intermediate vertical tubular member. Said intermediate vertical tubular member can be a copper tube 3 cooled by a water jacket 4 as illustrated in FIG. 1 and topped by a refractory ring 5. What is thus created, in the central part of the nozzle beneath the tundish member, is a volume without any liquid metal within which it is possible to carry out additions via an injection channel. One or several support arms are located on the upper part of the dome 2 to secure it to said refractory ring 5. The water-cooled copper tube 3 forms a heat exchanger that extracts heat from the liquid steel. As a consequence, the superheat of the liquid steel is drastically reduced close or even below the liquidus temperature.
A powder can be injected in the center of the hollow jet created by the refractory dome 2. This injection technique is disclosed in the document EP 0 605 379 B1. This powder injection aims to create an additional cooling of the liquid steel by the melting of the metallic powder or to modify the composition of the steel during casting by addition of other metallic elements such as ferro-alloys. As disclosed in document EP 2 099 576 B1, the powder can be transported via a mechanical screw feeder and is fed by gravity through one of the support arms of the refractory dome and through the refractory dome itself.
In the present application the term HJN equipment will be understood as describing the elements as described in FIG. 1 excepting the powder container 10 and the powder feeder 11.
During casting sequences using the HJN as previously described the equipment has to be frequently stopped because of the irregular flow of the liquid steel from the tundish 1 to the mould 9 and/or because of the irregular injection of powder, implying instability of the casting process and which could lead to the clogging of the HJN or to the clogging of the outlet of the powder injector.